Preparation of alpha-olefin polymers of relatively narrow molecular weight distribution

ABSTRACT

A catalyst composition for polymerizing alpha-olefins is prepared by treating a carrier containing OH groups with a liquid solution containing an excess of an organomagnesium composition with respect to the OH groups and contacting the thus-formed magnesium-containing carrier with a hydrocarbyl alcohol and at least one transition metal compound. Prior to contacting the magnesium-containing carrier with the alcohol, most of the liquid must be removed therefrom, so that it comprises not more than about 6% of the liquid. The amount of the transition metal compound is such that the molar ratio thereof to magnesium in the reaction mixture is about 0.3 to about 0.9. Also disclosed is a process for polymerizing alpha-olefins in the presence of the catalyst of the invention.

This is a divisional of a copending application Ser. No. 815,845, filed on Jan. 3, 1986, now U.S. Pat. No. 4,668,650.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for polymerizing alpha-olefins, a catalyst for such a polymerization method and a method for producing such a catalyst. A particular aspect of the present invention relates to a method for preparing a catalyst which produces linear low density polyethylene (LLDPE) having a relatively narrow molecular weight distribution, as evidenced by relatively low values of melt flow ratios (MFR), suitable for film and injection molding applications.

2. Description of the Prior Art

Linear low density polyethylene polymers possess properties which distinguish them from other polyethylene polymers, such as homopolymers of polyethylene. Certain of these properties are described in Anderson et al. U.S. Pat. No. 4,076,698.

Karol et al., U.S. Pat. No. 4,302,566, describe a process for producing certain linear low density polyethylene polymers in a gas phase, fluid bed reactor.

Graff, U.S. Pat. No. 4,173,547, Stevens et al., U.S. Pat. No. 3,787,384, Strobel et al., U.S. Pat. No. 4,148,754, and Ziegler, deceased, et al., U.S. Pat. No. 4,063,009, each describe various polymerization processes suitable for producing forms of polyethylene other than linear low density polyethylene, per se.

Graff, U.S. Pat. No. 4,173,547, describes a supported catalyst obtained by treating a support with both an organoaluminum compound and an organomagnesium compound followed by contacting this treated support with a tetravalent titanium compound.

Stevens et al., U.S. Pat. No. 3,787,384, and Strobel et al., U.S. Pat. No. 4,148,754, describe a catalyst prepared by first reacting a support (e.g., silica containing reactive hydroxyl groups) with an organomagnesium compound (e.g., a Grignard reagent) and then combining this reacted support with a tetravalent titanium compound. According to the teachings of both of these patents, no unreacted organomagnesium compound is present when the reacted support is contacted with the tetravalent titanium compound.

Ziegler, deceased, et al., U.S. Pat. No. 4,063,009, describe a catalyst which is the reaction product of an organomagnesium compound (e.g. an alkylmagnesium halide) with a tetravalent titanium compound. The reaction of the organomagnesium compound with the tetravalent titanium compound takes place in the absence of a support material.

A vanadium-containing catalyst, used in conjunction with triisobutylaluminum as a co-catalyst, is disclosed by W. L. Carrick et al. in Journal of American Chemical Society, Volume 82, page 1502 (1960) and Volume 83, page 2654 (1961).

Nowlin et al., U.S. Pat. No. 4,481,301, the entire contents of which are incorporated herein by reference, disclose a supported alpha-olefin polymerization catalyst composition prepared by reacting a support containing OH groups with a stoichiometric excess of an organomagnesium composition, with respect to the OH groups content, and then reacting the product with a stoichiometric excess of a tetravalent titanium compound with respect to the organomagnesium composition and the OH groups.

Dombro, U.S. Pat. No. 4,378,304, discloses an alpha-olefin, especially ethylene, polymerization catalyst prepared by reacting, in sequence: (1) a porous support with Group IIA organometallic compound, preferably a dialkylmagnesium compound; (2) reacting the composite of (1) with water or a hydrocarbyl alcohol; and (3) reacting the product of (2) with a Group IVB and/or VB transition metal compound(s).

It is a primary object of the present invention to prepare a high activity catalyst for the polymerization of alpha-olefins which yields products having a relatively high bulk density and a relatively narrow molecular weight distribution suitable for films and injection molding applications.

It is an additional object of the present invention to provide a catalytic process for polymerizing alpha-olefins which yields linear low density polyethylene of a relatively high bulk density and relatively narrow molecular weight distribution.

SUMMARY OF THE INVENTION

A supported alpha-olefin polymerization catalyst composition of this invention is prepared in a multi-step process. In the first step, a solid, porous carrier having reactive OH groups is contacted with a liquid containing at least one organomagnesium composition of the empirical formula

R_(n) MgR'.sub.(2-n)

where R and R' are the same or different and they are C₁ -C₁₂ hydrocarbyl groups, provided that R' may also be a halogen and n is 0, 1 or 2. The number of moles of the organomagnesium composition is in excess of the number of moles of the reactive OH groups on the carrier.

In the second step, the liquid is carefully evaporated to assure that none or very little of magnesium-containing compound(s) is removed from the reaction mixture and that most, if not all, of the magnesium-containing compound(s) are retained on the carrier. The product of this step is a solid, supported magnesium (Mg) composition.

Subsequently, the product is dried, in the third step, until it comprises not more than about 6% by weight of the liquid. The product of this step is a dry, free-flowing powder.

In the fourth synthesis step, the dry, free-flowing powder is contacted with at least one hydrocarbyl alcohol of the formula

R"OH

wherein R" is a C₁ -C₁₀ alkyl, alkenyl, aryl, alkaryl or aralkyl group.

In the fifth and final synthesis step, the product of the fourth step is reacted with at least one transition metal compound soluble in a non-polar solvent. The amount of the transition metal compound used in this step is such that the molar ratio of the transition metal to magnesium (Mg) in the reaction mixture of this step is about 0.3 to about 0.9, both the transition metal and Mg being calculated as elemental metals. The supported magnesium composition is substantially insoluble in the non-polar solvent. Accordingly, a reacted form of transition metal insoluble in the non-polar solvent becomes supported on the carrier.

The invention is also directed to an alpha-olefin polymerization process conducted in the presence of the catalyst of this invention.

DETAILED DESCRIPTION OF THE INVENTION

The polymers prepared in the presence of the catalyst of this invention are linear polyethylenes which are homopolymers of ethylene or copolymers of ethylene and higher alpha-olefins. The polymers have relatively high bulk density, and exhibit relatively high values of melt index (I₂) and relatively low values of melt flow ratio (MFR) and polydispersity, both defined below, as compared to similar polymers prepared in the presence of similar, previously-known catalyst compositions, e.g., those disclosed by Nowlin et al., U.S. Pat. No. 4,481,301. Thus, the polymers prepared with the catalyst compositions of this invention are especially suitable for the production of high strength films and injection molding applications. The polymers prepared with the catalyst compositions of this invention also have a relatively low level of hexane extractables, thereby making them suitable for the production of food packaging materials.

Catalysts produced according to the present invention are described below in terms of the manner in which they are made.

Suitable carrier materials, organomagnesium compositions, liquids, and the manner of using thereof in the first step of the catalyst synthesis are those disclosed by Nowlin et al., U.S. Pat. No. 4,481,301. Accordingly, only the most important features of such materials and of the manner of conducting the first catalyst synthesis step will be discussed herein.

The carrier materials have the form of particles having a particle size of from about 0.1 micron to about 200 microns, more preferably from about 10 to about 150 microns. Preferably, the carrier is in the form of spherical particles, e.g., spray dried silica. The internal porosity of the carriers is larger than 0.2 cm³ /gm, preferably larger than about 0.6 cm³ /gm. The specific surface area of the carriers is larger than about 50 m² /gm, preferably from about 150 to about 1500 m² /gm. In the most preferred embodiment, the carrier is silica which has been dehydrated by fluidizing with nitrogen and heating at about 800° C. for about 16 hours to achieve a surface hydroxyl concentration of about 0.4 mmols/gm. The silica of the most preferred embodiment is a high surface area, amorphous silica (surface area=300 m² /gm; pore volume of 1.65 cm³ per gram), and it is a material marketed under the tradename of Davison 952 or Davison 955 by the Davison Chemical Division of W. R. Grace and Company. The silica is in the form of spherical particles, e.g., as obtained by a spray-drying process.

Chemically bound water, e.g., as represented by the presence of the OH groups in the carrier, may be present when the carrier is contacted with water-reactive organomagnesium compounds in accordance with the present invention. Excess OH groups present in the carrier may be removed by heating the carrier, prior to the contacting step, for a sufficient time at a sufficient temperature to accomplish the desired degree of the OH groups removal. A relatively small number of OH groups is removed by sufficient heating at from about 150° C. to about 250° C., whereas a relatively large number of OH groups may be removed by sufficient heating at at least 500° or 600° C., preferably from about 750° C. to about 850° C. The heating is continued for about 4 to about 16 hours. The amount of the hydroxyl groups in silica may be determined according to the method disclosed by J. B. Peri and A. L. Hensley, Jr., in J. Phys. Chem., 72 (8), 2926 (1968), the entire contents of which are incorporated herein by reference.

While heating is the most preferred means of removing OH groups inherently present in many carriers, such as silica, the OH groups may also be removed by other removal means, such as chemical means. For example, a desired proportion of OH groups may be reacted with a suitable chemical agent, such as a hydroxyl reactive aluminum compound, e.g., triethylaluminum.

A dehydrated carrier material is treated with a solution of a solid organomagnesium composition in a liquid, the organomagnesium composition being capable of reacting with a transition metal compound soluble in non-polar solvents. In a preferred embodiment, the carrier material is admixed with a hydrocarbon, preferably a saturated hydrocarbon, such as hexane or isopentane, and the resulting suspension of the carrier is vigorously stirred before it is contacted with the solution of the organomagnesium composition in the liquid. In this preferred embodiment, the carrier suspension is continuously stirred while the solution of the organomagnesium composition is added thereto. After the addition is completed, the solution is refluxed for about 0.1 to about 10, preferably about 0.5 to about 5, and most preferably about 1.0 to about 2.0 hours, at a temperature of about 25 to about 200, preferably about 50 to about 100, and most preferably about 60° to about 80° C. The organomagnesium composition has the empirical formula R_(n) MgR'.sub.(2-n), where R and R' are the same or different and they are C₁ -C₁₂ hydrocarbyl groups, preferably C₁ -C₁₂ alkyl groups, more preferably C₁ -C₁₂ unsubstituted alkyl groups, yet more preferably C₁ -C₄ alkane groups and most preferably C₂ -C₄ alkane groups, R' is a halogen, preferably chlorine, bromine or iodine, and most preferably chlorine, and n is 0, 1 or 2.

Preferably, the carrier is treated with the aforementioned solution in such a manner that, after the treatment is completed, the carrier has magnesium incorporated into the pores thereof. As used herein, the concept of incorporating a material onto a carrier is intended to encompass the incorporation of the material (e.g., magnesium or transition metal compositions) onto the carrier by physical or chemical means. Accordingly, the incorporated material need not necessarily be chemically bound to the carrier. As a result of this treatment, magnesium becomes incorporated into the pores of the carrier by chemical or physical means. More particularly, the magnesium is incorporated into the pores of the carrier by: (1) a chemical reaction of the organomagnesium composition with the carrier, (2) a precipitation of magnesium from the organomagnesium composition onto the carrier or (3) a combination of such a reaction and precipitation.

Suitable liquids which are solvents for the organomagnesium composition, which may be a Grignard reagent, are ethers, such as aliphatic ethers, e.g., diethyl ether, diisopropyl ether, dibutyl ether, dipentyl ether, and ethyl-n-butyl ether and cyclic ethers, such as tetrahydrofuran and dioxane. Thus, the liquid medium containing the organomagnesium composition is usually an ether, preferably tetrahydrofuran.

It is important for the purposes of the present invention that the number of moles of the organomagnesium composition in the solution used to contact the carrier be in excess of the number of moles of the OH groups on the carrier, so that the molar ratio of the organomagnesium composition in the solution to the hydroxyl groups is greater than 1.0, preferably it is from about 1.1 to about 3.5, more preferably from about 1.5 to about 3.5, and most preferably from about 2.0 to about 3.5.

It is also important for the purposes of the present invention, that the number of moles of the sum of all magnesium-containing compounds on the carrier, in the product of the second and third steps of the catalyst synthesis of this invention, be in excess of the number of moles of the OH groups originally present on the carrier, prior to the contact of the carrier with the liquid containing the organomagnesium composition. The molar ratio of the sum of all magnesium-containing compounds in the product of the second and third steps to the aforementioned OH groups is greater than 1, preferably it is from about 1.1 to about 3.5, more preferably about 1.5 to about 3.5, and most preferably from about 2.0 to about 3.5.

To assure that most, if not all, of the magnesium-containing compound(s) are retained on the carrier, the liquid is removed from the reaction vessel with care to assure that none or very little magnesium-containing compound(s) is removed with it. The liquid may be removed by any means assuring that substantially all of the magnesium-containing compound(s) remain on the carrier, e.g., by distillation of the mixture of the impregnated carrier and the solvents, evaporation, decantation or centrifugation. Evaporation at about the boiling point of the liquid is the most preferred method of liquid removal. It is also important that the product of the second and third reaction steps is not subjected to washing or rinsing, so that the excess of the magnesium-containing compound or compounds which did not react with the hydroxyl (OH) groups of the carrier is retained on the carrier.

After the liquid is removed, the resulting product is dried, in the third synthesis step, by any conventional means, e.g., drying at ambient temperature or at 50°-80° C. for about 12-16 hours with a stream of dry nitrogen to produce a dry, free-flowing powder. The drying step is conducted until the resulting dry, free-flowing powder comprises not more than about 6%, preferably not more than about 5%, and most preferably about 2% to about 5% by weight of the liquid used to dissolve the organomagnesium composition prior to the addition thereof to the silica in step (i) of the synthesis. Without wishing to be bound by any theory of operability, it is believed that the presence of higher amounts of the liquid or solvent in the dry, free-flowing powder causes the resulting catalyst composition to produce polymers having undesirably high densities.

In the fourth synthesis step, the powder is contacted with at least one hydrocarbyl alcohol of the formula R" OH wherein R" is a C₁ -C₁₀ alkyl, cycloalkyl, alkenyl, aryl, alkaryl or aralkyl group, preferably a C₁ -C₁₀ alkyl or alkenyl group and most preferably C₁ -C₁₀ alkyl group.

Suitable alkyl alcohols are methanol, ethanol, propanol, isopropanol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, n-pentyl alcohol, isopentyl alcohol, tert-pentyl alcohol, n-hexyl alcohol, n-heptyl alcohol, n-octyl alcohol, and n-decyl alcohol. Suitable cycloalkyl alcohols are cyclobutanol, cyclopentanol, cyclohexanol and cycloheptanol.

Suitable alkenyl alcohols are allyl alcohol (also known as 1-pentenol), 1-buteneol, and 3-butene-2-ol.

Benzyl alcohol is a suitable aryl alcohol, and α- and β-phenylethyl alcohols are suitable alkaryl alcohols.

Methanol, ethanol, propanol and isopropanol are preferred alcohols, and ethanol is the most preferred alcohol.

The manner of contacting the powder with the alcohol is not critical. Thus, the powder may be contacted with a neat alcohol; the powder may be slurried in a suitable solvent and the slurry contacted with the alcohol; or the alcohol may be dissolved in a suitable solvent and the solution contacted with the powder. In a preferred embodiment, the powder is slurried in a non-polar solvent at a temperature and for a time sufficient to produce a substantially homogeneous slurry and then the slurry is contacted with the alcohol. In this preferred embodiment, the alcohol is preferably dissolved in a non-polar solvent, most preferably the same solvent which was used to produce a slurry of the magnesium-containing, dry, free-flowing powder. The amount of the hydrocarbyl alcohol is such that the molar ratio R"OH/Mg is about 0.1 to about 10, preferably about 0.3 to about 2, and most preferably about 0.3 to about 1.0. This reaction takes place at an ambient temperature, although higher temperatures, e.g. 50°-100° C., may be used.

Without wishing to be bound by any theory of operability, it is believed that the alcohol treatment produces catalyst compositions which polymerize resins, which, when formulated into films and other packaging products, have greater strength and lower hexane extractables than the products produced with similar catalyst compositions prepared without the alcohol-treatment step. Additionally, the resins produced wih the catalyst compositions of this invention have substantially higher bulk density than the resins produced with similar catalyst compositions prepared without the alcohol-treatment step, e.g., see a co-pending, commonly-assigned U.S. Application of Lo et al., Ser. No. 816,091, filed on Jan. 3, 1986, now U.S. Pat. No. 4,677,087.

The amount of magnesium-containing compound(s) which is incorporated onto the carrier should be sufficient to react with the transition metal, to incorporate a catalytically effective amount of the transition metal on the carrier in the manner set forth hereinbelow. Thus, the carrier should comprise from about 0.1 to about 50, preferably about 0.1 to about 5 millimoles (mmoles) of magnesium per gram of carrier (after the treatment of the carrier with the organomagnesium composition is completed). When the liquid containing the organomagnesium composition is contacted with the carrier, the amount of magnesium in this liquid is substantially the same as that stated above which is incorporated onto the carrier.

The product of the fourth step is reacted with at least one transition metal compound. This reaction is usually conducted in a non-polar solvent by forming a slurry of the product of the fourth step in the non-polar solvent. The transition metal compound is soluble in the non-polar solvent, while the treated carrier (i.e., the free-flowing powder treated with the hydrocarbyl alcohol), including the magnesium-containing compound(s), is insoluble therein. Thus, the reaction which takes place between the transition metal and the reactive magnesium-containing compound(s) is a reaction of a solid with a liquid. It is further noted that the reacted transition metal is insoluble in the non-polar solvent.

Without wishing to be bound by any theory of operability, it is thought that the reaction which takes place between the magnesium compound which is not a reaction product of an organomagnesium composition with the carrier and the transition metal in the solvent is substantially an oxidation/reduction reaction, wherein the magnesium compound acts as a reducing agent for the transition metal. On the other hand, while not wishing to be bound by any particular theory or chemical mechanism, the reaction which takes place between (1) the transition metal and (2) the reaction product of an organomagnesium composition and carrier containing reactive OH groups is not an oxidation/reduction reaction. However, it is noted that both of the above-mentioned reactions lead to the incorporation of transition metal onto the carrier.

Suitable transition metal compounds used herein are compounds of metals of Groups IVA, VA, VIA or VIII of the Periodic Chart of the Elements, as published by the Fisher Scientific Company, Catalog No. 5-702-10, 1978, providing that such compounds are soluble in non-polar solvents. Non-limiting examples of such compounds are titanium and vanadium halides, e.g., titanium tetrachloride, TiCl₄, vanadium tetrachloride, VCl₄, vanadium oxytrichloride, VOCl₃, titanium and vanadium alkoxides, wherein the alkoxide moiety has a branched or unbranched alkyl radical of 1 to about 20 carbon atoms, preferably 1 to about 6 carbon atoms. The preferred transition metal compounds are titanium compounds, preferably tetravalent titanium compounds. The most preferred titanium compound is titanium tetrachloride.

Mixtures of such transition metal compounds may also be used and generally no restrictions are imposed on the transition metal compounds which may be included. Any transition metal compound that may be used alone may also be used in conjunction with other transition metal compounds.

Suitable non-polar solvents, also referred to herein as liquid medium diluents, are materials in which the transition metal compounds are at least partially soluble and which are liquid at reaction temperatures. Preferred diluents are alkanes, such as hexane, n-heptane, octane, nonane, and decane, although a variety of other materials including cycloalkanes, such as cyclohexane, aromatics, such as benzene and ethylbenzene, and halogenated aromatics, such as chlorobenzene or ortho-dichlorobenzene, can be employed. As is obvious to those skilled in the art, mixtures of solvents may also be used. The most preferred solvent is n-hexane. Prior to use, the solvent should be purified, such as by percolation through silica gel and/or molecular sieves, to remove traces of water, oxygen, polar compounds, and other materials capable of adversely affecting catalyst activity.

The slurry of the fourth step is contacted with the transition metal compound, as described above, at a temperature and for a time sufficient to yield a solid catalyst component. Temperatures at which this reaction is conducted range from about -40° to about 250° C., preferably, from about 0° to about 170° C., and most preferably, the reaction is conducted at a temperature of about 25° to about 100° C. Suitable reaction times range from about 1/2 to about 25 hours, with about 1/2 to about 6 hours being preferred.

The reaction of the transition metal in the non-polar solvent with the magnesium-containing carrier material conveniently takes place by heating the non-polar solvent containing the organomagnesium composition and alcohol-treated carrier material and the transition metal compound to a suitable reaction temperature, e.g., to the reflux temperature of the solvent at standard atmospheric pressure. Thus, the reaction usually takes place under reflux conditions.

The various reaction parameters can be widely varied, suitable selection of such parameters being well within the skill of those having ordinary skill in the art. The concentration of the transition metal compound in the solution is, for example, from about 0.1 to about 5 Molar. It is important, however, that the molar amount of the transition metal compound in the solution is such that the molar ratio of the transition metal to magnesium (Mg) is about 0.3 to about 0.9, preferably about 0.4 to about 0.8, and most preferably about 0.5 to about 0.8. It is also believed, without wishing to be bound by any theory of operability, that the transition metal:Mg molar ratios outside of this range would produce a catalyst composition which, when used to polymerize alpha-olefins, would yield polymers having lower than desired values of I₂ and higher than desired values of MFR.

To assure that most, if not all, of the transition-metal-containing compound(s) are retained in the product of the last catalyst synthesis step, the non-polar solvent is removed from the reaction vessel with care to assure that none or very little of the transition-metal-containing compounds(s) is removed with it. The solvent may be removed by any means assuring that substantially all of the transition-metal-containing compound(s) remain on the carrier, e.g., by distillation of the mixture of the solvent and the solid reaction product, evaporation, decantation or centrifiguration. Evaporation at about the boiling point of the solvent is the most preferred method of the solvent removal. It is also important that the product of the fifth synthesis step is not subjected to washing or rinsing to avoid inadvertent removal of any transition-metal-containing compound(s) therefrom.

The lack of the washing or decantation steps, usually present in prior art (e.g., see Nowlin et al, U.S. Pat. No. 4,481,301), assures that substantially all of the transition metal compound(s) present in step (v) are retained on the final catalyst composition. The resulting catalyst composition produces polymers having relatively low MFR values and relatively high bulk density, as compared to the aforementioned catalyst compositions of Nowlin et al. The lack of the washing or decantation steps also eliminates the potentially hazardous transition-metal-containing waste products.

As indicated above, the catalysts of the present invention are prepared in the substantial absence of water, oxygen, and other catalyst poisons. Such catalyst poisons can be excluded during the catalyst preparation steps by any well known methods, e.g., by carrying out the preparation under an atmosphere of nitrogen, argon or other inert gas. An inert gas purge can serve the dual purpose of excluding external contaminants during the preparation and removing undesirable reaction by-products resulting from the preparation of the neat, liquid reaction product. Purification of any diluent employed in the first and fourth preparative steps in the manner described above is also helpful in this regard.

The thus-formed supported catalyst may be activated with suitable activators, also known as co-cocatalysts or catalyst promoters. The activators are known in the art and they include any of the materials commonly employed as promoters for olefin polymerization catalyst components containing compounds of the Group IB, IIA, IIB, IIIB and IVB of the Periodic Chart of the Elements, published by Fisher Scientific Company, Catalog Number 5-702-10, 1978. Examples of such promoters are metal alkyls, hydrides, alkylhydrides, and alkylhalides, such as alkyllithium compounds, dialkylzinc compounds, trialkylboron compounds, trialkylaluminum compounds, alkylaluminum halides and hydrides, and tetraalkylgermanium compounds. Mixtures can also be employed. Specific examples of useful promoters include n-butyllithium, diethylzinc, di-n-propylzinc, triethylboron, triethylaluminum, triisobutylaluminum, tri-n-hexylaluminum, ethylaluminum dichloride, dibromide, and dihydride, isobutyl aluminum dichloride, dibromide, and dihydride, diethylaluminum chloride, bromide, and hydride, di-n-propylaluminum chloride, bromide, and hydride, diisobutylaluminum chloride, bromide, and hydride, tetramethylgermanium, and tetraethylgermanium. Organometallic promoters which are preferred for use according to this invention are Group IIIB metal alkyls and dialkylhalides having 1 to about 20 carbon atoms per alkyl radical. More preferably, the promoter is a trialkylaluminum compound having 1 to about 6 carbon atoms per alkyl radical, and the most preferred promoter is triethylaluminum.

The organometallic promoter is employed in an amount which is at least effective to promote the polymerization activity of the solid component of the catalyst of this invention. Preferably, at least about three parts by weight of the promoter are employed per part, by weight, of solid catalyst component, although higher ratios, such as 10:1, 25:1, 100:1 or higher, are also suitable and often give highly beneficial results. In slurry polymerization processes, a portion of the promoter can be employed to pretreat the polymerization medium if desired. Other promoters which can be used herein are disclosed in Stevens et al., U.S. Pat. No. 3,787,384, column 4, line 45 to column 5, line 12, and in Strobel et al., U.S. Pat. No. 4,148,754, column 4, line 56 to column 5, line 59, the entire contents of both patents being incorporated herein by reference.

The catalyst may be activated in situ by adding the activator and catalyst separately to the polymerization medium. It is also possible to combine the catalyst and activator before the introduction thereof into the polymerization medium, e.g., for up to about 2 hours prior to the introduction thereof into the polymerization medium at a temperature of from about -40° to about 100° C.

A suitable activating amount of the activator may be used to promote the polymerization activity of the catalyst. The aforementioned proportions of the activator can also be expressed in terms of the number of moles of activator per gram atom of transition metal in the catalyst of, e.g., from about 1 to about 100 and preferably greater than about 5.

Alpha-olefins may be polymerized with the catalysts prepared according to the present invention by any suitable process. Such processes include polymerizations carried out in suspension, in solution or in the gas phase. Gas phase polymerization reactions are preferred, e.g., those taking place in stirred bed reactors and, especially, fluidized bed reactors.

The molecular weight of the polymer may be controlled in a known manner, e.g., by using hydrogen. With the catalysts produced according to the present invention, molecular weight may be suitably controlled with hydrogen when the polymerization is carried out at relatively low temperatures, e.g., from about 30° to about 105° C. This control of molecular weight may be evidenced by a measurable positive change in melt index (I₂) of the polymer produced.

The molecular weight distribution of the polymers prepared in the presence of the catalysts of the present invention, as expressed by the melt flow ratio (MFR) values, varies from about 20 to about 32 for LLDPE products having a density of about 0.900 to about 0.940, and an I₂ melt index of about 4 to about 100. As is known to those skilled in the art, such MFR values are indicative of a relatively narrow molecular weight distribution of the polymer. As is also known to those skilled in the art, such MFR values are indicative of the polymers especially suitable for injection molding applications since the polymers having such MFR values exhibit relatively low amounts of warpage and shrinkage on cooling of the injection molded products. The relatively low MFR values of the polymers prepared with the catalysts of this invention also indicate that they are suitable for the preparation of various film products since such films are likely to have excellent strength properties. MFR is defined herein as the ratio of the high load melt index (HLMI or I₂₁) divided by the melt index (I₂), i.e.,

    MFR=I.sub.21 /I.sub.2

Smaller MFR values indicate relatively narrower molecular-weight distribution polymers.

Another measure of polymer's molecular weight distribution is polydispersity, defined as the ratio of weight average moleclar weight (M_(w)) and number average molecular weight (M_(n)), i.e.,

    polydispersity=M.sub.w /M.sub.n

Polymers prepared with the catalyst compositions of the present invention have polydispersity values of about 3-4.5. As is known to those skilled in the art, such polydispersity values also indicate a relatively narrow molecular weight distribution, thereby confirming the suitability of the polymers for injection molding and film applications.

The catalysts prepared according to the present invention are highly active and may have an activity of at least about 500-10,000 grams of polymer per gram of catalyst per 100 psi of ethylene in about 3 hours.

The linear polyethylene polymers prepared in accordance with the present invention may be homopolymers of ethylene or copolymers of ethylene with one or more C₃ -C₁₀ alpha-olefins. Thus, copolymers having two monomeric units are possible as well as terpolymers having three monomeric units. Particular examples of such polymers include ethylene/1-butene copolymers, ethylene/1-hexene copolymers, ethylene/1-octene copolymers, ethylene/4-methyl-1-pentene copolymers, ethylene/1-butene/1-hexene terpolymers, ethylene/propylene/1-hexene terpolymers and ethylene/propylene/1-butene terpolymers. When propylene is employed as a comonomer, the resulting linear low density polyethylene polymer preferably has at least one other alpha-olefin comonomer having at least four carbon atoms in an amount of at least 1 percent by weight of the polymer. Accordingly, ethylene/propylene copolymers are possible, but not preferred. The most preferred comonomer is 1-hexene.

The linear low density polyethylene polymers produced in accordance with the present invention preferably contain at least about 80 percent by weight of ethylene units.

A particularly desirable method for producing linear low density polyethylene polymers according to the present invention is in a fluid bed reactor. Such a reactor and means for operating the same is described by Levine et al., U.S. Pat. No. 4,011,382, and Karol et al., U.S. Pat. No. 4,302,566, the entire contents of both of which being incorporated herein by reference, and by Nowlin et al, U.S. Pat. No. 4,481,301.

The following Examples further illustrate the essential features of the invention. However, it will be apparent to those skilled in the art that the specific reactants and reaction conditions used in the Examples do not limit the scope of the invention.

EXAMPLE 1 (Synthesis of Inventive Catalyst Composition)

All procedures were carried out in glass or quartz equipment under purified nitrogen using predried nitrogen-purged solvents.

Catalyst Preparation

First Step

150 grams of Davison silica gel Grade 955 (a trademark of and available from the Davison Chemical Division of W. R. Grace and Company, Baltimore, Md.) heated at 800° C. in the atmosphere of dry nitrogen for 16 hours, was placed into a 2-liter flask under a slow nitrogen purge. Approximately 1.5 liters of hexane was added while stirring and the contents were heated to reflux. 95 mls of a 2.0 molar solution of ethylmagnesium chloride in tetrahydrofuran (THF) was added dropwise to the refluxing solution, while the solution was stirred. The reflux was continued for one hour.

Second Step

The solvents were removed by distillation at 80° C. for 60 minutes.

Third Step

The product was dried at 80° C. for about 16 hours under a slow nitrogen-purge atmosphere.

Yield: 190 grams; Mg=1.03 mmols/gram; THF=0.63 mmols/gram (4.55% by weight of the product).

Fourth Step

121.9 grams of the third step product, containing 125.6 mmols Mg, was slurried in 800 mls of dry hexane. 3.26 grams of anhydrous ethanol (70.8 mmols) in 100 mls of hexane was added to the slurry (alcohol/Mg mole ratio=0.56).

Fifth Step

The slurry was heated to reflux and 9.4 mls of TiCl₄ (85.6 mmols) was added thereto. The reflux was continued for one (1) hour, the solvent was removed by distillation and the product was dried overnight at 60° C. in nitrogen atmosphere. Yield: 135.8 grams of product which analyzed as follows: Mg=0.844 mmols/gm; Ti=0.598 mmols/gm; Cl=2.68 mmols/gm; THF=0.50 mmols/gm.

COMPARATIVE EXAMPLES A-C

Three more catalyst samples, prepared substantially in accordance with the teachings of Nowlin et al., U.S. Pat. No. 4,481,301, were used in comparative testing as discussed in Examples summarized below. These catalysts are referred to herein as "Comparative A, B or C" catalysts or simply as "A, B or C" catalysts, respectively.

First Step

30.36 grams of Davison silica gel, Grade 955 (dried at 800° C. for 16 hours) was placed into a 500 ml four-neck reaction flask fitted with a dropping funnel, water condenser, dry nitrogen line, and overhead stirrer. Under a slow nitrogen purge, 275 ml of dry hexane was added to the silica while stirring. The silica/hexane slurry was brought to the reflux temperature and 18.2 ml of 2.1 molar ethylmagnesium chloride in THF (EtMgCL/THF) solution was added dropwise (about 8 minutes) and the reflux was continued for an additional 60 minutes. After this time, the solvents were removed by distillation and the silica dried at 80° C. under a nitrogen purge. Product yield: 36.41 grams; Mg content: 1.06 mmols/gm; THF: 0.69 mmols/gram (5% by weight); Cl: 1.08 mmols/gram.

Second Step

10.02 grams of the product from the first step (10.62 mmols Mg) was placed into a 500 ml flask under a slow nitrogen purge. 100 ml of hexane containing 4.4 ml of TiCl₄ (40.06 mmols Ti) was added to the flask and the slurry was heated to reflux for about 2 hours. The slurry was transferred to a filter apparatus, filtered while at 60° C., and washed with 500 ml of dry hexane to remove excess TiCl₄. Yield: 9.96 grams of product which analyzed as follows: Mg: 0.97 mmols/gram; Ti: 0.60 mmols/gram; Cl: 3.25 mmols/grams; THF: 0.43 mmols/gram.

The catalyst of comparative Example B was prepared in substantially the same manner as the comparative A catalyst, except that the molar Ti:Mg ratio in the second step was 4.0.

The comparative catalyst C was prepared by slurrying 175.1 grams of the product of the third step of Example 1 into about 1600 mls of heptane containing 77 mls of TiCl₄ (701 mmols of Ti). The slurry was refluxed for two (2) hours, the temperature was lowered to 60° C., and the slurry was filtered and washed with 600 ml aliquots of hexane five times to remove unreacted TiCl₄. The product was dried in a stream of nitrogen at 60° C. for 8 hours. Yield: 191.3 grams of product which analyzed as follows: Mg=0.87 mmols/gm; Ti=0.59 mmols/gm; Cl=2.97 mmols/gm; THF=0.24 mmols/gm.

Table A, below, summarizes the pertinent parameters of comparative Examples A, B and C catalyst compositions.

                  TABLE A                                                          ______________________________________                                                         2nd Step Amounts of Ingredients                                Catalyst        Ti/Mg    In Catalyst Compositions                              of              Mole     (mmols/gram of catalyst)                              Example                                                                               Type     Ratio    Ti    Mg    Cl    THF                                 ______________________________________                                         A      Excess   3.8      0.60  0.97  3.25  0.43                                       TiCl.sub.4                                                              B      Excess   4.0      0.69  0.92  3.37  0.27                                       TiCl.sub.4                                                              C      Excess   3.9      0.59  0.87  2.97  0.24                                       TiCl.sub.4                                                              ______________________________________                                    

COMPARATIVE EXAMPLES D-G

Four additional comparative catalyst examples were prepared wherein the alcohol-treatment step was omitted. These comparative catalyst compositions are substantially the same as those disclosed in a co-pending, commonly-assigned patent application of Lo et al., Ser. No. 816,091, filed on Jan. 3, 1986, now allowed U.S. Pat. No. 4,677,087.

Comparative Example D--Catalyst Preparation

First Step

30.36 grams of Davison silica gel Grade 955 (a trademark of and available from the Davison Chemical Division of W. R. Grace and Company, Baltimore, Md.) heated at 800° C. in the atmosphere of dry nitrogen for twelve hours, was placed into a 500 ml flask under a slow nitrogen purge. Approximately 275 ml of hexane was added while stirring and the contents were heated to reflux. 18.2 ml of a 2.1 molar solution of ethylmagnesium chloride (C₂ H₅ MgCl) in tetrahydrofuran (THF) was added dropwise to the refluxing solution while the solution was stirred. The reflux was continued for one hour.

Second Step

The solvents were removed by distillation at 65° C. for 60 minutes.

Third Step

The product was dried at 80° C. for about 18 hours in nitrogen atmosphere.

Yield: 36.41 grams; Mg=1.06 mmols/gram; THF=0.694 mmols/gram (5% by weight); Cl=1.08 mmols/gram.

Fourth Step

10.07 grams of the product from the first step (10.67 mmols Mg) was placed into a 500 ml flask under a slow nitrogen purge. 100 ml of hexane containing 0.6 ml of TiCl₄ (5.46 mmols Ti) was added to the flask and the slurry was heated to reflux for about 2 hours. The solvent was removed by distillation and the product was dried overnight at 60° C. in nitrogen atmosphere. Yield: 8.89 grams of product which analyzed as follows: Mg=0.86 mmols/gram; Ti=0.48 mmols/gram; Cl=2.57 mmols/gram; THF=0.49 mmols/gram.

Comparative catalyst compositions of Examples E-G were prepared in substantially the same manner except that the quantities of C₂ H₅ MgCl, TiCl₄ and THF were varied. Table B, below, summarizes the pertinent parameters of Comparative Examples E-G catalyst compositions synthesis.

    ______________________________________                                                            4th Step Amounts of Ingredients in                          Catalyst           Ti/Mg    Catalyst Compositions                              of                 Mole     (mmols per gram of catalyst)                       Example                                                                               Type        Ratio    Ti   Mg    Cl   THF                                ______________________________________                                         D      No excess TiCl.sub.4                                                                       0.5      0.48 0.86  2.57 0.49                                      No Alcohol                                                              E      No excess TiCl.sub.4                                                                       0.3      0.30 ˜0.90                                                                          --   --                                        No Alcohol                                                              F      No excess TiCl.sub.4                                                                       0.5      0.46 0.89  2.70 0.58                                      No Alcohol                                                              G      No excess TiCl.sub.4                                                                       0.7      0.70 ˜0.90                                                                          --   --                                        No Alcohol                                                              ______________________________________                                    

COMPARATIVE EXAMPLES H-1 THROUGH H-8

Eight more catalyst samples, prepared substantially in accordance with the teachings of Nowlin et al., U.S. Pat. No. 4,481,301, were used in comparative testing as discussed in Examples summarized below. In the synthesis of these catalysts, a greater amount of THF was left in the product of the first synthesis step of catalysts H-1 and H-2 than in the Example 1 catalyst or in comparative A-G catalysts. The THF content was progressively reduced in the product of the first synthesis step to prepare catalysts H-3 through H-8. These catalysts are referred to herein as "Comparative H-1 through H-8" catalysts or simply as "H-1 through H-8" catalysts.

First Step

94.5 grams of Davison silica gel, Grade 952 (dried at 800° C. for 16 hours) was placed into a 2 liter four-neck reaction flask fitted with a dropping funnel, water condenser, dry nitrogen line, and overhead stirrer. Under a slow nitrogen purge, 950 ml of dry hexane was added to the silica while stirring. The silica/hexane slurry was brought to the reflux temperature and 60 ml of 1.85 molar ethylmagnesium chloride in THF (EtMgCl/THF) solution was added dropwise (about 8 minutes) and the reflux was continued for an additional 60 minutes. After this time, the solvents were removed by distillation and the silica dried for 1.5 hours at 80° C. under a nitrogen purge. Product yield: 108 grams; Mg content (Theory): 1.03 mmols/gm.

Eight separate samples of this product were dried under increasingly more severe conditions to remove various amounts of THF, as summarized in Table A, below.

                  TABLE A                                                          ______________________________________                                         Sample Drying Conditions  THF Content wt (%)                                   ______________________________________                                         A001   1.5 Hrs. at 80° C.                                                                         6.1                                                  A002   3.0 Hrs. at 80° C.                                                                         5.2                                                  A003   7.5 Hrs. at 80° C.                                                                         4.6                                                  A004   18.5 Hrs. at 80° C.                                                                        4.2                                                  A005   18.5 Hrs. at 80° C. and                                                                    4.2                                                         4 Hrs. at 80° C. under vacuum                                    A006   18.5 Hrs. at 80° C. and                                                                    3.7                                                         30 Hrs. at 100° C.                                               A007   18.5 Hrs. at 80° C. and                                                                    3.4                                                         30 Hrs. at l20° C.                                               A008   18.5 Hrs. at 80° C. and                                                                    2.8                                                         30 Hrs. at 140° C.                                               ______________________________________                                    

Second Step

The products of the first step were then reacted with TiCl₄ in the second step, exemplified here for the first step product of Sample A001, to prepare eight catalyst samples H-1 through H-8.

6.48 grams of sample A001 from the first step (6.67 mmols Mg) was placed into a 300 ml flask under a slow nitrogen purge. 63 mls of heptane containing 3.15 ml of TiCl₄ (28.7 mmols Ti) was added to the flask and the slurry was heated to reflux for about one hour. The slurry was transferred to a filter apparatus, filtered at about 70° C., and washed with 500 ml of dry hexane to remove excess TiCl₄ and produce the H-1 catalyst.

Yield: 6.69 grams of product which analyzed as follows: Mg (Theory): 0.99 mmols/gram; THF 0.85 mmols/gram (6.1 wt. %).

Seven additional catalysts, H-2 through H-8, were prepared from the products of the first step, designated A002 through A008, respectively, in substantially the same manner as the H-1 catalyst.

EXAMPLES 2-20 (Preparation of LLDPE Products)

Linear low density polyethylene products were prepard in a 1.6 liter autoclave. In a typical experiment (Example 2), the autoclave was heated under a nitrogen purge to about 100° C. for one-half hour and then cooled to ambient temperature. About 1000 mls of hexane, and 135 grams of 1-hexene and 2.0 ml of triethylaluminum (25 weight percent solution in hexane) were added while stirring at about 900 rpm. (The total volume of hexane and hexene was about 1.2 liters in each experiment.) The catalyst was prepared by adding about 0.060 grams of the catalyst of Example 1 to a dry, nitrogen blanketed stainless steel catalyst addition flask containing about 50 ml of dry hexane. The reactor was closed, heated to 50° C. and the internal pressure was increased to 27.5 psi with hydrogen. The reactor temperature was increased to about 70° C. and ethylene was introduced at 121 psi total pressure. After the autoclave was filled with ethylene, the contents of the catalyst addition flask were added with a slight ethylene pressure to the autoclave.

The ethylene flow was monitored through a Hastings Mass Flowmeter NALL-50KG/CC-420 interfaced to a strip chart recorder to record ethylene flow (gms/minute) as a function of time (minutes).

At the end of the polymerization time, about 45 minutes, the autoclave was cooled to room temperature, opened and the contents placed in a large container. About 300 ppm of Irganox 1076 was added as a hexane solution and volatiles allowed to evaporate under a hood. Polymer yield was about 161 grams.

Tables I and IC summarize the polymerization conditions and properties of the products. 1-hexene was used as a comonomer in all Examples. Density values reported in Tables I and IC are density values corrected to an I₂ melt index value of 1.0 according to the method of Elston, U.S. Pat. No. 3,645,992, the entire contents of which are incorporated herein by reference.

                                      TABLE I                                      __________________________________________________________________________     SUMMARY OF LLDPE PRODUCTS                                                      Catalyst Synthesis and Polymerization Conditions                                  Cata-                                                                              Catalyst           Produc-                                              Ex-                                                                               lyst                                                                               Synthesis          tivity           Product                             am-                                                                               of  Ti:Mg          H.sub.2 /C.sub.2                                                                   (gm   C.sub.6 /C.sub.2                                                                   Polymeriza-                                                                           Polymer    MFR                                                                               Density               ple                                                                               Exam-                                                                              Mole Alcohol Used                                                                             Mole                                                                               polymer)                                                                             Mole                                                                               tion Time                                                                             Yield      (I.sub.21 /                                                                       Corrected             No.                                                                               ple Ratio                                                                               Type Amount                                                                              Ratio                                                                              (gm cat/hr)                                                                          Ratio                                                                              (Minutes)                                                                             (grs.)                                                                              I.sub.2                                                                           I.sub.21                                                                          I.sub.2)                                                                          (gms/cc)              __________________________________________________________________________     2  1   0.7  Ethanol   0.184                                                                              3580  1.91                                                                               45     161  2.43                                                                              74.4                                                                              30.6                                                                              0.931                 3  1   0.7  Ethanol   0.181                                                                              3580  2.31                                                                               50     167  4.00                                                                              121.7                                                                             30.4                                                                              0.927                 4  E   0.3  None      0.282                                                                              1370  1.76                                                                               53     56   8.10                                                                              245.0                                                                             30.2                                                                              0.931                 5  E   0.3  None      0.282                                                                              1660  1.76                                                                               49     64.5 5.90                                                                              198.0                                                                             33.5                                                                              0.929                 6  D   0.5  None      0.184                                                                              5400  1.90                                                                               30     163  6.20                                                                              186.0                                                                             29.9                                                                              0.922                 7  D   0.5  None      0.184                                                                              5340  1.91                                                                               40     131  4.00                                                                              117.0                                                                             29.1                                                                              0.924                 8  G   0.7  None      0.184                                                                              4720  1.91                                                                               50     144  2.60                                                                              76.9                                                                              29.6                                                                              0.928                 9  G   0.7  None      0.282                                                                              4240  1.76                                                                               36     152  10.80                                                                             372.0                                                                             29.8                                                                              0.922                 10 B   4.0  None      0.282                                                                              4830  1.76                                                                               32     43   2.30                                                                              81.1                                                                              35.2                                                                              0.930                 11 B   4.0  None      0.184                                                                              4650  1.91                                                                               35     175  1.93                                                                              68.4                                                                              35.4                                                                              0.922                 12 A   3.8  None      0.184                                                                              4440  1.91                                                                               65     127  1.99                                                                              68.6                                                                              34.5                                                                              0.920                 __________________________________________________________________________

    TABLE IC       SUMMARY OF LLDPE PRODUCTS Polymerization Conditions Product*    THF      Content      Produc-        In First Reaction   Polymeri- Polymer tivity         *Density Example Catalyst Catalyst Step Pro- Ti/Mg Comonomer  zation      Time Yield (gm PE/gm   MFR Corrected No. Of Example (grs) duct (wt %)      Mole Ratio Type C.sub.n /C.sub.2 (minutes) (gms) cat./hr) I.sub.2      I.sub.21 (I.sub.21       /I.sub.2) (gms/cc)                                      13 H-1 0.146      6.1 4.3 1-Hexene 1.42 120 229 785 1.37 45.0 32.9 0.9282 14 H-2 0.100 5.2      4.3 1-Hexene 1.42 120 203 920 2.55 85.6 33.6 0.9271 15 H-3 0.149 4.6 4.3      1-Hexene 1.42 129 269 840 2.80 90.8 32.4 0.9258 16 H-4 0.092 4.2 4.3      1-Hexene 1.42 47 103 1430 2.51 86.5 34.5 0.9190 17 H-5 0.101 4.2 4.3      1-Hexene 1.42 28 151 3200 2.07 69.8 33.7 0.9244 18 H-6 0.105 3.7 4.3      1-Hexene 1.42 79 214 1545 3.04 99.4 32.7 0.9239 19 H-7 0.186 3.4 4.3      1-Hexene 1.42 66 216 1055 2.11 71.3 33.8 0.9 20 H-8 0.208 2.8 4.3      1-Hexene 1.42 56 274 1410 2.98 103 24.6 0.9218      *Conditions: 1.0 liter hexane, 80° C. 90 grams lhexene, 900 rpm,      total pressure 140 psi.

The data of Examples 13-20 shows that catalysts with better 1-hexene incorporation (as evidenced by polymer products obtained therewith having lower density) and higher productivity are obtained when most of the THF used in the first catalyst synthesis step is removed so that the product of that step contains not more than about 6.0% by weight of the THF.

The weight molecular weight (M_(w)) and number average molecular weight (M_(n)) of the polymers produced in Examples 2, 6 and 12 were determined by Gel permeation chromatography. From these values, the values of polydispersity, which is the ratio of M_(w) /M_(n), were calculated. The results are summarized in Table II.

                  TABLE II                                                         ______________________________________                                                         Catalyst                                                              Catalyst Synthesis                                                      Example                                                                               of       Ti:Mg                                                          No.    Example  Mole Ratio                                                                               M.sub.w                                                                               M.sub.n                                                                               M.sub.w /M.sub.                        ______________________________________                                                                                 n                                      2      1        0.7       37932  20500  4.30                                   6      D        0.5       69518  15125  4.60                                   12     A        3.8       91331  16110  5.67                                   ______________________________________                                    

EXAMPLES 21-23 (LLDPE Produced In Fluid Bed Reactor)

The performance of scaled up version of the catalysts of Examples 1, C and F was compared under substantially identical operating conditions in a fluidized-bed, pilot reactor. This comparison was accomplished by producing copolymers at the same melt index and density and then observing the physical properties of each resin produced. The resins were copolymers of ethylene and 1-hexene having a density of about 0.918 gm/cc and an I₂ melt index of about 2.0.

The experiments were done in a pilot-scale fluidized-bed reactor which was 18 inches in diameter and capable of producing up to 50 lb/hr of resin. The only difference between the pilot plant preparation of the catalyst of Example C and the laboratory procedure (described earlier) was that a solvent decantation followed by several solvent washes was substituted for the filtration. The results are summarized in Table III.

                  TABLE III                                                        ______________________________________                                                      Alcohol Used                                                      Example Catalyst            Alcohol:Mg                                                                             Bulk Density                               No.     Of Example Type     Mole Ratio                                                                             lbs/ft.sub.3                               ______________________________________                                         21      1          Ethanol  0.58    22.6                                       22      F          None             21.5; 21.2                                 23      C          None             21.1; 20.9                                 ______________________________________                                    

The data of Table III indicates that the alcohol-modified catalysts of this invention produce resins having higher bulk density than the comparative catalyst compositions prepared without the alcohol-modification step. As is known to those skilled in the art, higher bulk density materials have more efficient handling characteristics in commercial-scale operations.

The data of Tables II and III illustrates that the use of a hydrocarbyl alcohol in catalyst synthesis produces catalyst compositions which polymerize polymers having melt flow ratio values of about 30.0 and polydispersity values of about 4.3. In contrast, comparative catalyst compositions A and B, prepaed with a molar excess of titanium with respect to magnesium and without the use of alcohol, produce polymers having melt flow ratios of about 34.8±0.4 and a polydispersity of 5.67, suggesting a broader molecular weight distribution.

As is known to those skilled in the art, polymers having lower MFR values usually exhibit better mechanical properties and lower hexane extractables which renders them more suitable for applications requiring FDA (Food and Drug Administration) approval. The term "hexane extractables" is used herein to define the amount of a polymer sample extracted by refluxing the sample in hexane in accordance with the FDA-approved procedure. As is known to those skilled in the art, the FDA requires that all polymer products having food contact contain less than 5.5% by weight of such hexane extractables.

Comparative catalyst compositions D-G produce polymers with poorer physical properties, higher hexane extractables, slightly broader molecular weight distribution and a lower bulk density. It will be apparent to those skilled in the art that the specific embodiments discussed above can be successfully repeated with ingredients equivalent to those generically or specifically set forth above and under variable process conditions.

From the foregoing specification, one skilled in the art can readily ascertain the essential features of this invention and without departing from the spirit and scope thereof can adapt it to various diverse applications. 

We claim:
 1. A process for preparing a polymer of at least one C₂ -C₁₀ alpha-olefin, the polymer having a density of 0.94 g/cc or less, comprising conducting the polymerization in the presence of a catalyst prepared by a process comprising the steps of:(i) contacting a solid, porous carrier having reactive OH groups with an ether containing at least one organomagnesium composition having the empirical formula:

    R.sub.n MgR'.sub.(2-n)

where R and R' are the same or different C₁ -C₁₂ hydrocarbyl groups, provided that R' may also be a halogen and n is 0, 1, or 2, the number of moles of said organomagnesium composition being in excess of the number of moles of said OH groups on said carrier, whereby said organomagnesium composition is reacted with said OH groups on said carrier; (ii) removing said ether, whereby a supported magnesium (Mg) composition in the form of a solid powder is formed; (iii) drying said solid powder, without washing or rinsing thereof, until it comprises not more than about 6% by weight of the ether; (iv) contacting the product of step (iii) with at least one hydrocarbyl alcohol of the formula R"OH wherein R" is a C₁ -C₁₀ alkyl, alkenyl, aryl, alkaryl or aralkyl group; (v) contacing the product of step (iv) with a titanium compound soluble in a non-polar solvent, the number of moles of said titanium compound being such that the molar ratio of titanium (Ti) to magnesium (Mg) is about 0.3 to about 0.9, both the Ti and Mg being calculated as elemental metals, said supported magnesium composition being substantially insoluble in said non-polar solvent, whereby a reacted form of titanium which is insoluble in said non-polar solvent becomes supported on said carrier; (vi) removing said non-polar solvent without washing or rinsing of the product of step (v); and (vii) activating the product of the step (vi) with a catalyst activator containing compounds of Group IB, IIA, IIB, IIIB or IVB of the Periodic Chart of the Elements.
 2. A process of claim 1 wherein the drying in step (iii) is conducted until the solid powder comprises less than about 5% by weight of the ether.
 3. A process of claim 2 wherein the drying is conducted until the solid powder comprises about 2% to about 5% by weight of the ether.
 4. A process of claim 3 wherein molar ratio of the Ti to Mg in step (iv) is about 0.4 to about 0.8.
 5. A process of claim 4 wherein the molar ratio of the Ti to Mg in step (iv) is about 0.5 to about 0.8.
 6. A process of claim 5 wherein R" is a C₁ -C₁₀ alkyl or alkenyl group.
 7. A process of claim 6 wherein R" is a C₁ -C₁₀ alkyl group.
 8. A process of claim 7 wherein the alcohol is methanol, ethanol, propanol or isopropanol.
 9. A process of claim 8 wherein the alcohol is ethanol.
 10. A process of claim 9 wherein n is
 1. 11. A process of claim 10 wherein step (i) comprises:(a) slurrying the carrier in a non-Lewis base liquid; and (b) adding to the slurry resulting from said step (a) the organomagnesium composition in the form of the ether solution thereof.
 12. A process of claim 11 wherein the ether is tetrahydrofuran.
 13. A process of claim 12 wherein the porous, solid carrier is silica, alumina or combinations thereof.
 14. A process of claim 13 wherein the porous, solid carrier is silica.
 15. A process of claim 14 wherein the titanium compound is a tetravalent titanium compound.
 16. A process of claim 15 wherein the tetravalent titanium compound is TiCl₄.
 17. A process of claim 16 wherein, in step (i), the ratio of the number of moles of said organomagnesium composition to the number of moles of the OH groups on said silica is from about 1.1 to about 3.5.
 18. A process of claim 17 wherein, in step (i), the ratio of the number of moles of said organomagnesium composition to the number of moles of the OH groups on said silica is from about 1.5 to about 3.5.
 19. A process of claim 18 wherein, in step (i), the ratio of the number of moles of said organomagnesium composition to the number of moles of the OH groups on said silica is from about 2.0 to about 3.5.
 20. A process of claim 19 wherein the tetrahydrofuran is evaporated in step (ii) at about 75° to about 90° C. for about 12 to about 20 hours.
 21. A process of claim 20 wherein the tetrahydrofuran is evaporated at about 80° to about 85° C. for about 16 hours in a dry nitrogen atmosphere.
 22. A process of claim 21 wherein said steps (iv) and (v) are conducted by, in step (iv), slurrying the product of step (iii) in a non-polar solvent and contacting the resulting slurry with said hydrocarbyl alcohol, and, in step (v), contacting the slurry with said transition metal compound.
 23. A process of claim 22 wherein, in said step (vi), said non-polar solvent is evaporated at about 75° to about 90° C. for about 12 to about 20 hours.
 24. A process of claim 23 wherein said non-polar solvent is evaporated at about 80° to about 85° C. for about 16 hours in a dry nitrogen atmosphere.
 25. A process of claim 24 wherein said non-polar solvent is an alkane, cycloalkane or aromatics halogenated aromatics.
 26. A process of claim 25 wherein said non-polar solvent is hexane.
 27. A process of claim 26 wherein, prior to contacting the silica in step (i), it is heated at a temperature of about 750° C. to about 850° C. for at least four hours.
 28. A process of claim 27 wherein the organomagnesium composition is ethylmagnesium chloride.
 29. A process of claim 28 wherein said liquid is removed in said step (ii) by evaporation at about the boiling point of the liquid.
 30. A process of claim 29 wherein, in said step (vi), said non-polar solvent is removed by evaporation at about the boiling point of the solvent.
 31. A process of claim 30 wherein the molar ratio of the Ti to Mg in step (iv) is 0.7.
 32. A process of claim 31 wherein the polymer is a copolymer of ethylene and at least one C₃ -C₈ alpha-olefin.
 33. A process of claim 32 wherein the polymer is a copolymer of ethylene and 1-hexene.
 34. A process of claim 1 wherein the solid powder in said step (iii) is dried at an ambient temperature or at 50°-80° C. for about 12-16 hours with a stream of dry nitrogen. 